(1) Field of the Invention
The present invention relates to a liquid crystal television receiver and a liquid crystal display device.
(2) Description of the Related Art
A liquid crystal display device such as a liquid crystal television receiver includes a backlight constituted by a discharge lamp which consumes relatively high electric power. When such a liquid crystal display device is kept powered on without any image signal inputted, the backlight is held on while a cell opening ratio of a liquid crystal panel of the display device is minimum, resulting in waste of electric power at the backlight.
To solve this problem, there has been proposed a technique, as disclosed in JP-A-2006-13942, in which when input of image signals from an external input terminal has been suspended for a predetermined continuous time period with the external input terminal selected through a remote control device or others, a controller outputs a control signal to a backlight drive circuit to turn off a part of a plurality of discharge lamps that is other than a discharge lamp or lamps opposed to characters or a figure displayed by an OSD (on-screen display) processing portion.
Further, JP-A-7-39174 discloses a technique where power is inputted from a dc battery to a backlight via an emitter-collector of a transistor. In this technique, when a predetermined time is elapsed after input from a tuner is suspended, a base voltage of the transistor is lowered to lower an input voltage to the backlight so as to decrease the value of a tube current of the backlight. A similar technique is disclosed in JP-A-8-237579 in which an illuminance of a backlight is lowered by lowering an electric power supplied to the backlight. JP-A-2006-140647 discloses a technique where a backlight control circuit stepwise drops a voltage supplied to a backlight.
However, the technique of JP-A-2006-13942 has a drawback that much time is taken to resume operation of the display device upon an image signal is inputted again after input of image signals is suspended, since the discharge lamp itself is turned off during the suspension. In addition, when the discharge lamp having been off is turned on upon the resuming of operation, the luminance varies among the discharge lamps, more specifically, between the discharge lamp(s) having been on and the other discharge lamp(s) having been off. This makes a user feel uncomfortable.
On the other hand, the technique of JP-A-7-39174 is inapplicable to a high-voltage line supplying a relatively high voltage, since the electric power is supplied via a transistor. Thus, the technique can not be used with a backlight driven at a high voltage. More specifically, although a voltage required for turning on a LED is about 2V, voltages required for turning a hot cathode tube and a cold cathode fluorescent tube, respectively, are as high as about 70V-140V and about 200V-1000V, which the technique of JP-A-7-39174 is incompatible with. JP-A-8-237579 and JP-A-2006-140647 do not teach any circuit configuration specifically.